Inevitably, the physical output of any CAD-based manufacturing process will differ from the input model. That is true for any manufacturing process, whether it’s machining, molding, stamping, casting, forging, or 3D printing. Deviation from the CAD model may be minimal, but it is there! Sometimes that’s acceptable, sometimes it’s not. It is the role of the manufacturing engineer to find the optimal solution that meet time, cost, and quality requirements.

With industry 4.0, closed-loop manufacturing becomes crucial in providing a competitive advantage to manufacturers, helping them get the most of their manufacturing processes. Using the latest 3D measurement technology, it’s now easier than ever to quickly get accurate dimensional information on manufactured parts. The challenge is to be able to feed that information back (upstream) into the manufacturing process to make corrections and “close” the manufacturing loop.

In a recent exercise Polyrix demonstrated how dimensional information acquired by 3D scanning a 3D metal printed part can assist in correcting the input CAD model to obtain a significantly more accurate part printed in a single iteration. The part selected for printing came from the NIST MBE-PMI Validation Model Library (CTC-02)1. A first sample was printed and measured using a high-accuracy PolyScan XS Surround 3D Scanner2.

Comparison between the output scan data and original CAD input revealed surface deviation induced by the 3D printing process. Those deviations were in the range of 0.250mm and displayed on the physical part using Polyrix’s Live Inspection deviation projection software.

After quantifying surface deviations induced by the 3D printing process on a single part, and before making any adjustments, a further 5 sample parts were scanned to make sure the deviation pattern was consistent. Analysis of the samples using PolyWorks Inspector software and Surface Data SPC tool, an average deviation colormap and a standard deviation colormap were obtained.

The average deviation colormap showed a similar pattern to the first sample scanned. The standard deviation colormap showed that the 3D-printing process consistently induce deviations into the same areas of the part. In the attempt of getting a 3D-printed part closer to the desired CAD, a technique called morphing was used to correct the CAD model. Simply put, the CAD model surface was moved up where the physical part was too low, and vice-versa.

The morphed model of the CAD was generated using the Polyrix Polyview Software using the original CAD and 3D deviation information output by the PolyScan XS.

This corrected (morphed) CAD model was then sent back for 3D printing. The resulting 3D printed part was scanned and compared to the original CAD model; the deviation in most areas were under 0.050-0.075mm a 5 fold reduction in measured errors than the original printed part.

In conclusion, the Polyrix project demonstrated how the output of a 3D printing process can be significantly improved in a single iteration, using 3D scanning data to morph the input CAD model. The role of 3D measurement should go beyond simply informing if a part is good or bad, it should provide corrective information to improve the manufacturing process.